<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>dynamic-shadow</title>
    <style>
        .dynamic-shadow {
            position: relative;
            width: 10rem;
            height: 10rem;
            background: linear-gradient(75deg,#6db1ff,#063bad);
            z-index: 1;
        }
        .dynamic-shadow::after {
            content:"";
            width: 100%;
            height: 100%;
            background: inherit;
            top: 0.5rem;
            position: absolute;
            opacity: .7;
            z-index: -1;
            filter: blur(.4rem);
        }
    </style>
</head>
<body>
    <div class="dynamic-shadow"></div>
</body>
</html>